Two-pass evaporator

ABSTRACT

A two-pass evaporator suitable for use in an automobile includes various pressure drop devices to aliquot refrigerant into tubes that make up the two-pass evaporator. The two-pass evaporator includes a first pressure-drop device configured to receive and expand a liquid phase refrigerant into a first mixture of two-phase refrigerant; and a second pressure-drop device configured to receive and expand the first mixture of two-phase refrigerant into a second mixture of two-phase refrigerant and aliquot the second mixture of two-phase refrigerant to the first end of the first plurality of tubes. The two-pass evaporator includes a transition manifold that may house a flow-modulation plate disposed therein and configured to segregate the transition manifold into an upstream portion and a downstream portion. The flow-modulation device works in conjunction with the upstream pressure drop devices to aliquot refrigerant from the first plurality of tubes to the second plurality of tubes.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application that claims thebenefit under 35 U.S.C. §120 of U.S. patent application Ser. No.14/069,878 filed Nov. 1, 2013, the entire disclosure of which is herebyincorporated herein by reference.

TECHNICAL FIELD OF INVENTION

This disclosure generally relates to a two-pass evaporator, and moreparticularly relates to features within the two-pass evaporator thataliquot refrigerant across the tubes that are part of the two-passevaporator.

BACKGROUND OF INVENTION

An air-conditioning system for a motor vehicle typically includes arefrigerant loop having an evaporator located within a heating,ventilation, and air-conditioning (HVAC) module for supplyingconditioned air to the passenger compartment, an expansion devicelocated upstream of the evaporator, a condenser located upstream of theexpansion device in front of the engine compartment, and a compressorlocated within the engine compartment upstream of the condenser. Theabove mentioned components are hydraulically connected in series withinthe closed refrigerant loop.

The compressor compresses and circulates a refrigerant through theclosed refrigerant loop. Starting from the inlet of the evaporator, alow pressure two-phase refrigerant having mixture of liquid and vaporenters the evaporator and flows through the tubes of the evaporatorwhere it expands into a low pressure vapor refrigerant by absorbing heatfrom an incoming air stream. The low pressure vapor refrigerant thenexits the outlet of the evaporator and enters the compressor where it iscompressed into a high pressure high temperature vapor. The highpressure vapor refrigerant then flows through the condenser where itcondenses into a high pressure liquid refrigerant by releasing the heatto the ambient air outside the motor vehicle. The condensed highpressure liquid refrigerant is returned to the evaporator through theexpansion device, which expands the high pressure liquid refrigerant toa low pressure, low temperature mixture of liquid-vapor refrigerant torepeat the cycle.

A conventional multi-pass evaporator includes an inlet manifold, anoutlet manifold, and a plurality of tubes hydraulically connecting themanifolds. Additionally, there may be one or more intermediate ortransition manifolds, that interconnect groups of tubes between theinlet and outlet manifold. It is desirable to aliquot, that isdistribute into as equal parts as much as possible, two-phaserefrigerant to the tubes of the evaporator to provide uniform cooling ofthe airstream. If two-phase refrigerant enters the inlet manifold at arelatively high velocity, the liquid phase of the refrigerant is carriedby momentum of the flow further away from the entrance of the inletmanifold to the distal end of the inlet manifold. For relatively highvelocity, the tubes closest to the inlet manifold entrance may receivepredominantly the vapor phase and the tubes near the distal end of theinlet manifold receive predominantly the liquid phase. On the otherhand, if the two-phase refrigerant enters the inlet manifold at arelatively low velocity, the tubes closest to the inlet manifoldentrance may receive predominantly the liquid phase and the tubes nearthe distal end of the inlet manifold may receive predominantly the vaporphase. In either case, this results in the undesirable misaliquoting ofthe refrigerant flowing through the tubes.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a two-pass evaporator suitable foruse in an automobile is provided. The two-pass evaporator includes aninlet manifold, a transitional manifold, an outlet manifold, a firstpressure drop device, and a second pressure drop device. The inletmanifold is configured to define a chamber for containing refrigerant,define an inlet port for receiving refrigerant into the chamber, andhydraulically couple the inlet port to a first end of a first pluralityof tubes. The transition manifold is configured to hydraulically couplea second end of the first plurality of tubes to a first end of a secondplurality of tubes arranged parallel to the first plurality of tubes.The outlet manifold is located proximate to the inlet manifold. Theoutlet manifold is configured to define an outlet port and hydraulicallycouple a second end of the second plurality of tubes to the outlet port.The first pressure-drop device is located proximate to the inlet port.The first pressure-drop device is configured to receive and expand aliquid phase refrigerant into a first mixture of two-phase refrigerant.The second pressure-drop device located within the inlet manifold. Thesecond pressure-drop device is configured to receive and expand thefirst mixture of two-phase refrigerant into a second mixture oftwo-phase refrigerant and aliquot the second mixture of two-phaserefrigerant to the first end of the first plurality of tubes. The firstpressure-drop device and the second pres sure-drop device cooperate toform a hybrid expansion device.

In another embodiment, the transition manifold includes aflow-modulation plate disposed therein and configured to segregate thetransition manifold into an upstream portion and a downstream portion,and aliquot refrigerant from the first plurality of tubes to the secondplurality of tubes.

In yet another embodiment, the flow-modulation plate defines a pluralityof openings configured to aliquot refrigerant from the first pluralityof tubes to the second plurality of tubes.

Further features and advantages will appear more clearly on a reading ofthe following detailed description of the preferred embodiment, which isgiven by way of non-limiting example only and with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example withreference to the accompanying drawings, in which:

FIG. 1 shows a schematic of an air conditioning system with anevaporator having a hybrid expansion device;

FIG. 2 shows an exemplary two-pass evaporator having a hybrid expansiondevice;

FIG. 3 shows a cross-sectional view of the inlet manifold of theevaporator shown in FIG. 2; and

FIG. 4 shows a graph of data related to the evaporator of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a non-limiting example of an air conditioning system 10 havinga closed refrigerant loop 12 hydraulically connecting a compressor 14, acondenser 16, and a two-pass evaporator 100 in series. The two-passevaporator 100 includes a hybrid expansion device, hereafter the HED200, configured to provide uniform refrigerant aliquoting through thetwo-pass evaporator 100 for all operating refrigerant flow velocitiescaused by variations in the compressor 14 speed. The HED 200 includes afirst pressure-drop device such as a Low-Pressure Thermostatic ExpansionValve, hereafter the LP-TXV 202, and a second pressure-drop device suchas an Enhanced Orifice Tube, hereafter the EOT 204.

FIGS. 2 and 3 illustrate further details of the two-pass evaporator 100.The two-pass evaporator 100 includes an inlet manifold 102, an outletmanifold 104, and plurality of tubes 106 hydraulically connecting theinlet manifold 102 to the outlet manifold 104 for refrigerant flowtherebetween. The tubes 106 together with a transition manifold 105 todefine a U-shaped path for refrigerant flow from the inlet manifold 102to the outlet manifold 104, thereby enabling the inlet manifold 102 andoutlet manifold 104 to be placed in a side-by-side parallel arrangement.The inlet open ends 107 of the tubes 106 are inserted through slots 109positioned along the inlet manifold 102 for refrigerant flow from theinlet manifold 102 to the tubes 106. The inlet manifold 102 and outletmanifold 104 are shown above the tubes 106 with respect to the directionof gravity. A plurality of fins 108 is disposed between and materiallyjoined to the tubes 106 to facilitate heat exchange between therefrigerant and a stream of ambient air. The tubes 106 and fins 108 areformed of a heat conductive material, preferably an aluminum alloy,assembled onto the inlet manifold 102, the transition manifold 105, andthe outlet manifold 104 and brazed together to form the two-passevaporator heat exchanger assembly.

Shown in FIG. 3 is a cross-sectional view of the inlet manifold 102 ofthe two-pass evaporator 100 extending along a manifold axis A. The inletmanifold 102 includes an inlet port 110 for receiving the EOT 204, whichis configured to cooperate with the LP-TXV 202 to improve refrigerantaliquoting across tubes 106 of the two-pass evaporator 100. The LP-TXV202 expands a liquid refrigerant from the condenser into a first mixtureof two-phase refrigerant and the EOT 204 expands the first mixture intoa second mixture of two-phase refrigerant.

The EOT 204 may be disposed within the chamber defined by the inletmanifold 102, extending substantially along the length of the chamberand substantially parallel with the manifold axis A. The EOT 204includes an inlet end 214, a distal end 216 that may be a blind endopposite that of the inlet end 214, and a plurality of orifices 206therebetween. The inlet end 214 is in direct hydraulic connection withthe LP-TXV 202. The distal end 216 is typically mounted by capturing itin the end cap 117 of the inlet manifold 102. The plurality of orifices206 may be arranged in a linear array parallel to the manifold axis Aand oriented away from the inlet open ends 107 of the tubes 106,preferably 180 degrees from the inlet open ends 107 and substantially inthe opposite direction of gravity. As shown in FIG. 2, the in-vehicleposition is such that the inlet manifold 102 and the outlet manifold 104are at the top, the transition manifold 105 is at the bottom, and theevaporator face 112 is substantially perpendicular to the ground. In acase where the evaporator face 112 is tilted towards the ground, up to60° from the vertical, it is still preferable that the orifices 206 ofthe EOT 204 are substantially opposite to the gravity direction.

The HED 200 provides a two stage pressure drop, in which the totalpressure drop is apportioned between the LP-TXV 202 and the EOT 204 andis equivalent to the pressure drop of a conventional TXV. It wassurprisingly found that a controlled two stage pressure drop provided bythe LP-TXV and EOT working in unison, resulted in the improvedaliquoting of refrigerant through the tubes 106 of the two-passevaporator 100. The LP-TXV 202 is configured to provide a first mixtureof two-phase refrigerant to the EOT 204. The EOT 204 serves as aretention and expansion device where it retains and accumulates thefirst mixture of two-phase refrigerant until the liquid part of theincoming mixture substantially fills the interior volume of the EOT 204before being discharged through the orifices 206 as a second mixture oftwo-phase refrigerant, thereby aliquoting the refrigerant across thetubes 106.

Referring again to FIGS. 1 and 2, the two-pass evaporator 100, which issuitable for use in an automobile, includes an inlet manifold 102. Theinlet manifold is configured to define the chamber for containingrefrigerant, define the inlet port 110 for receiving refrigerant intothe chamber, and hydraulically couple the inlet manifold 110 to a firstend 120 of a first plurality of tubes 122. The transition manifold 105is configured to hydraulically couple a second end 124 of the firstplurality of tubes 122 to a first end 126 of a second plurality of tubes128 arranged parallel to the first plurality of tubes 122. As notedabove, this advantageously allows the outlet manifold 104 to be locatedproximate to the inlet manifold 102. The outlet manifold defines anoutlet port 132 and hydraulically couples a second end 130 of the secondplurality of tubes 128 to the outlet port 132.

The two-pass evaporator 100 includes a first pressure-drop device(LP-TXV 202) located proximate to the inlet port 110. The firstpressure-drop device is configured to receive and expand a liquid phaserefrigerant into a first mixture of two-phase refrigerant. The two-passevaporator 100 also includes a second pressure-drop device (EOT 204)located within the inlet manifold 102. The second pressure-drop deviceis configured to receive and expand the first mixture of two-phaserefrigerant into a second mixture of two-phase refrigerant and aliquotthe second mixture of two-phase refrigerant to the first end 120 of thefirst plurality of tubes 122. The first pressure-drop device and thesecond pressure-drop device cooperate to form a hybrid expansion device(HED 200).

It was discovered that temperature uniformity across the various tubescould be improved if the transition manifold 105 was equipped with aflow-modulation plate 134. The flow-modulation plate 134 is disposedgenerally within the transition manifold, and is configured to segregatea transition cavity 136 defined by the transition manifold 105 into anupstream portion 138 and a downstream portion 140. In one embodiment,the flow-modulation plate 134 includes or defines a plurality ofopenings 142 configured to aliquot refrigerant from the first pluralityof tubes to the second plurality of tubes.

While not subscribing to any particular theory, it is believed that theflow-modulation plate 134 provides flow restriction that better aliquotsrefrigerant flowing from the first plurality of tubes 122 to the secondplurality of tubes 128. The flow-modulation plate 134 creates a backpressure on the refrigerant from the first plurality of tubes 122 byrestricting the flow (i.e.—choking the flow) of refrigerant asrefrigerant moves from an upstream portion 138 to a downstream portion140. This causes better distribution of refrigerant in both the firstplurality of tubes 122 to the second plurality of tubes 128. Thisadvantage of the flow modulation plate further enhances the aliquotingfunctionality of the HED 200. If HED 200 performs its intended functionby aliquoting the two-phase refrigerant into the first plurality oftubes 122, the benefit realized by including the flow-modulation plate134 may be less evident and the size of the opening 142 in theflow-modulation plate 134 can be larger to offer less flow restriction.

By contrast, for an HED 200 that is designed to perform within aparticular flow range, if the refrigerant flow, and consequently thepressure drop across HED 200, is outside the design range, the HED 200may not be able to satisfactorily perform its aliquoting function. Also,for high refrigerant flows beyond the HED design range, an undesirablerefrigerant hiss or whistle noise may be generated. The noise isgenerated by refrigerant turning from liquid to vapor as the refrigerantemanates at high velocity from the orifices 206 in the EOT 204 of theHED 200. In general, if the HED 200 cannot deliver good flowdistribution due to some design constraint such as a noise limit, thenthe benefit of the flow-modulation plate 134 may be more useful. In thiscase, the flow-modulation plate 134 may have smaller sized openings 142and thus may offer higher flow resistance to the refrigerant, therebycompensating for what HED 200 could not achieve. The HED 200 functionscooperatively with the flow-modulation plate 134 to deliver good overallrefrigerant aliquoting with minimal refrigerant noise and across a widerrange of refrigerant flows. Together, the HED 200 and flow modulationplate 134 forms the hybrid flow modulation system (HFMS).

FIG. 4 is a graph 400 of test data showing performance of an evaporatorcomparable to the two-pass evaporator 100 described herein when equippedwith only the HED 200 (HED only 402), that is without the flowmodulation plate 134 (labeled FMD in FIG. 4); equipped with only theflow modulation plate 134 (FMD only 404), that is without the HED 200;the expected performance characteristics for a two-pass evaporatorequipped with both the HED 200 and the flow modulation plate 134(HED+FMD_Expected 406); and the actual performance characteristics forthe two-pass evaporator 100 equipped with both the HED 200 and the flowmodulation plate 134 (HED+FMD_Actual 408). The performancecharacteristics include an Air Temperature Inhomogeneity 410 and anEvaporator Effectiveness 420. The Air Temperature Inhomogeneity 410 isdetermined by calculating the difference between the maximum outlet airtemperature and the minimum outlet air temperature across the face ofthe two-pass evaporator. The Evaporator Effectiveness 420 is calculatedbased on a ratio of the heat transfer performance achieved by a givenheat exchanger to the maximum heat transfer performance theoreticallypossible, which in this instance is when outlet air temperature is equalto the temperature of the refrigerant flowing through the pass throughwhich air is coming out. The Air Temperature Inhomogeneity 410 for theHED+FMD_Expected 406 and the Evaporator Effectiveness 420 for theHED+FMD_Expected 406 are estimated based on the trend of data from testswith various evaporators with different aliquoting devices and also datafrom tests with different state-of-the-art evaporators used in theindustry. As can be seen, the actual performance characteristics (theHED+FMD_Actual 408) for the two-pass evaporator 100 described herein issurprisingly better than the expected result. This significantimprovement is believed to be due to an unexpected synergisticinteraction of the HED and FDM devices suggesting that the hybrid flowmodulation system (HFMS) possess a unique ability to aliquot refrigerantin both the passes of the evaporator to maximize the performance.

Accordingly, a two-pass evaporator 100 is provided. The two-passevaporator 100 includes several features that help to aliquotrefrigerant to the tubes 106 so that the temperature across the two-passevaporator 100 is more uniform.

While this invention has been described in terms of the preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow.

We claim:
 1. A two-pass evaporator suitable for use in an automobile,said two-pass evaporator comprising: an inlet manifold configured todefine a chamber for containing refrigerant, define an inlet port forreceiving refrigerant into the chamber, and hydraulically couple theinlet port to a first end of a first plurality of tubes; a transitionmanifold configured to hydraulically couple a second end of the firstplurality of tubes to a first end of a second plurality of tubes; anoutlet manifold located proximate to the inlet manifold, said outletmanifold configured to define an outlet port and hydraulically couple asecond end of the second plurality of tubes to the outlet port; a firstpressure-drop device located proximate to the inlet port, said firstpressure-drop device configured to receive and expand a liquid phaserefrigerant into a first mixture of two-phase refrigerant; a secondpressure-drop device located within the inlet manifold, said secondpressure-drop device configured to receive and expand said first mixtureof two-phase refrigerant into a second mixture of two-phase refrigerantand aliquot said second mixture of two-phase refrigerant to the firstend of the first plurality of tubes, wherein the first pressure-dropdevice and the second pressure-drop device cooperate to form a hybridexpansion device.
 2. The two-pass evaporator in accordance with claim 1,wherein the transition manifold includes a flow-modulation platedisposed therein and configured to segregate the transition manifoldinto an upstream portion and a downstream portion, and aliquotrefrigerant from the first plurality of tubes to the second plurality oftubes.
 3. The two-pass evaporator in accordance with claim 2, whereinthe flow-modulation plate defines a plurality of openings configured toaliquot refrigerant from the first plurality of tubes to the secondplurality of tubes.